1. Field of the Invention
The present invention relates to a device for displacement of movable parts on motor vehicles such as sliding roofs, windows or the like. More specifically, the present invention relates to such a device for displacement including an electrical servomotor mechanically coupled to the movable part and a supply circuit for braking the servomotor.
2. Description of the Related Art
Prior art devices of this type is generally illustrated in the published German Patent Application Nos. 1 914 580, 25 49 964, and 26 46 634. These devices for displacement are designed such that short circuit braking of the servomotor takes place when the movable part reaches a predetermined set position such as an end position. The movable part is moved out of this set position by the corresponding triggering of the servomotor.
Furthermore, a drive device for a part of a motor vehicle which can be adjusted between end positions is illustrated in U.S. Pat. No. 5,566,593 which includes an electric motor connected to a rack via a step-down gearing which has a worm wheel. The rack is located on a driven shaft and is drive-coupled via drive cables to the adjustable part. The electric motor is shut down by an operating mechanism in at least one predetermined position of the adjustable part. A ratchet wheel of an eccentric wheel gear is drive-coupled to the step-down gearing for activation of the operating mechanism. In this reference, the drive shaft, the driving part of the eccentric wheel gear, and the worm wheel are provided with form-fitting means which enable axial displacement of the drive shaft for emergency activation of the rack with simultaneous decoupling of the worm wheel and the drive shaft. This approach requires numerous mechanical parts so that production and installation costs are relatively high. In addition, there can be a high noise level during the operation of the device due to frictional rubbing of the parts.
A first object of the present invention is to devise a device for displacing movable parts on a motor vehicle which allows emergency activation of the movable parts with relatively low expenditure of force.
Another object of the present invention is to provide such a device for displacement of movable parts with relatively few mechanical components.
Yet another object of the present invention is to provide such a device which minimizes production costs and installation costs.
These and other objects are achieved by a device for displacement of movable parts on a motor vehicle in accordance with the present invention including an electrical servomotor which is permanently mechanically coupled to a movable part and a supply circuit adapted to operate the electrical servomotor, the supply circuit including an isolating means by which the supply circuit can be broken to prevent short circuit braking of the servomotor.
The permanent mechanical coupling of the servomotor and the movable part means that a clutch between the servomotor and the movable part is eliminated. During emergency activation of the movable part such as when the motor vehicle voltage fails, the present invention allows the movable part to be operated by hand with low expenditure of force because it is not necessary to work against a plug brake of the electrical servomotor.
In one embodiment, the direction of rotation of the servomotor is reversible in the conventional manner and there is provided a reversing operating mechanism in the supply circuit for selectively dictating the direction of rotation of the servomotor. Preferably, the isolating means and the reversing operating mechanism are coupled to one another such that in the normal operational state, i.e. when the displacement device is working properly, short circuit braking of the servomotor takes place in any position of the movable part. This ensures prompt and exact stopping of the movable part not only in predetermined positions such as the end positions, but also in any position therein between.
The isolating means can be located between a voltage supply and the reversing operating mechanism or alternatively, between the reversing operating mechanism and the servomotor, thereby yielding an especially compact, space-saving circuit design. The latter embodiment applies mainly when the isolating means is integrated into the reversing operating mechanism.
The isolating means is preferably designed such that upon failure of the feed voltage, the supply circuit is automatically broken. In such an embodiment, no additional action on the isolating means is necessary to prevent the plug brake and allow emergency activation of the movable part. In another embodiment, a structure for independently activating the isolating means may also be provided.
The isolating means may have at least one relay or solid-state switch such as a field effect transistor. Preferably, the isolating relay is provided with a contact which breaks the supply circuit when the isolating relay drops out. Alternatively, the solid-state switch is designed and arranged such that the solid-state switch disables automatically when the feed voltage fails.
In yet another embodiment of the present invention, the isolating means may include at least one manually operated switch, button, or a plug-and-socket connection which can be detached manually to break the supply circuit and terminate the short circuit braking. In this regard, the plug-and-socket connection can be made as a tension element and a fuse may be integrated into the plug-and-socket connection.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the invention when viewed in conjunction with the accompanying drawings.